the manta-fins produce a counter torque (outboard rolling moment, counter of the vehicles turn) that works to negate the de-stabilizing inboard torque produced by the SEAVIEW's sail and 'V' shaped 'Cadillac' fins at the stern. The manta-fins contribute to the dynamic roll stability of the SEAVIEW in a tight turn. As the submarines angle of attack about the yaw (turning) axis increases, and starts to 'skid' into a turn, a situation occurs at the manta-fin tips (those tips well below the vehicles longitudinal center of rotation) where the inboard manta-fin tip begins to generate an upward moment (force) and the outboard manta-fin tip produces a downward moment. These two forces induce a torsional moment that works to right the boat in the turn; the manta-fins improve the boats roll stability dynamically in a turn.
The significant maneuverability problems with this boat occur as a consequence of a turn while submerged. Sea-trails taught me to 'ease' the SEAVIEW into high speed submerged turns. To put the rudder hard over while running at any significant speed rolls the boat into an uncontrollable dive to the bottom. (American LOS ANGELES class attack submarines have the same problem). Other than that, and the SEAVIEW's woefully poor backing down ability, it handles pretty much like any other r/c submarine.
The only vice I can lay at the feet (fins) of the manta-fins is that they work to de-stabilize the boat in the pitch plane and contribute a great deal of flow and wave-making drag. The fix was to install permanent vanes within each propulsion nozzle, their job to direct the exhausted water upward, countering the pitching moment at the bow. In water tests verified that the fixed vanes countered the bow induced pitching problem throughout the SEAVIEW's speed regime, net angle change as a consequence of submerged speed was zero. Mission accomplished!
But, keep in mind that the two pitching forces (shape of the hull forward, the fixed vanes in the nozzles aft) are directed down; the net force on the vehicle is a downward one. However, this downward force acting on the submerged submarine is of low magnitude and is easily countered by operating the boat at a slight up-angle or simply by cranking in a bit of 'rise' on the sailplanes.
After installation of the fixed vanes in the nozzles depth control of the SEAVIEW became no more difficult than driving a 'traditional' type r/c submarine.
The SEAVIEW, as an r/c submarine, can be made to be dynamically stable in pitch and yaw as it travels submerged - without need of non-scale 'stabilizing' fins or control surfaces.
Nearly all modern American combat attack submarines employ a set of downward canted (anhedral) stabilizers at the stern (situated between the horizontal surfaces and lower rudder). Their primary function is to serve as foundations from which either evasion devices or towed cables are launched or streamed clear of the propeller/pump-jet disc. The secondary purpose of the stern mounted anhedral stabilizers is to generate a torsional force (created as the boat's angle of attack about the yaw axis increases) to counter the boats tendency to roll inboard in a turn. On a 'real' submarine this unwanted inboard rolling moment originates solely with the sail and a big reason that today's submarine sail structures are kept as short and low of area as possible. Sail structures are either well faired in to the hull (as practiced by the Russian 'Ruben' design bureau) or are so shaped as to limit the structures ability to produce lateral 'lift' at a high yaw angle of attack (American LOS ANGELELS class).
With the SEAVIEW we are cursed with three surfaces that produce a unified torsional moment in a turn: the large sail and two upward angled fins as the stern.
The rolling, and reduced turn rate experienced by the SEAVIEW underwater was observed and noted. Like any other type submarine I drive, I first work out the maximum underwater speed I can attain and still maintain depth control once the rudder is put hard over. Same test and observations as I work the horizontal control surfaced to maintain or change depth. The objective during these sea-trial activities is to determine the submarines 'performance envelop'. I determine the edges of that envelop and try not to exceed them during normal vehicle operation. Sea-trials are more than working out the mechanical bugs and trimming the boat, it is also that initial period of operation where you, the Driver, learn what you can and cannot do with the vehicle above and below the surface.
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